Not only did U.S. officials approve, allow and assist in the sale of more than 2,000 guns to the Sinaloa cartel -- the federal government used taxpayer money to buy semi-automatic weapons, sold them to criminals and then watched as the guns disappeared.

This disclosure, revealed in documents obtained by Fox News, could undermine the Department of Justice's previous defense that Operation Fast and Furious was a "botched" operation where agents simply "lost track" of weapons as they were transferred from one illegal buyer to another. Instead, it heightens the culpability of the federal government as Mexico, according to sources, has opened two criminal investigations into the operation that flooded their country with illegal weapons.